diff --git a/libavformat/os_support.h b/libavformat/os_support.h
index d4603632f7..f9a1706cb1 100644
--- a/libavformat/os_support.h
+++ b/libavformat/os_support.h
@@ -32,7 +32,7 @@
 #if defined(__MINGW32__) && !defined(__MINGW32CE__)
 #  include <fcntl.h>
 #  define lseek(f,p,w) _lseeki64((f), (p), (w))
-#endif
+#endif /* defined(__MINGW32__) && !defined(__MINGW32CE__) */
 
 static inline int is_dos_path(const char *path)
 {